1. Field of the Invention
The present invention generally relates to methods and resist compositions for increasing the resolution of photolithographic patterns and more specifically to an improved double-exposure technique for increasing photolithographic resolution.
2. Description of the Related Art
In optical lithography, the aerial image becomes degraded due to diffraction, especially with sub-half micron patterning. This limits the ultimate resolution of the lithography system. If the resolution of the aerial image is improved or sharpened, the process window can be widened and much smaller features can be formed.
The size reduction of features formed on wafers is limited by the resolution of the aerial image projected on the wafers. To improve resolution, conventional efforts were devoted to manipulating the illumination systems (e.g., off-axis and annular illumination) or to manipulating the masks (e.g., phase shift mask). However, manipulation of the illumination systems has disadvantages, such as loss of intensity and pattern distortion and/or artifacts. Similarly, phase-shift approaches impose stringent conditions on the circuit design, require the printing of high resolution sub-features and demanded special feature size and shape management, making the phase shift mask approach difficult and expensive.